The present invention relates to means for securing a plurality of core elements within the core of a nuclear reactor, particularly a fast breed reactor.
In the core of fast breed reactors, there are inserted nuclear fuel materials, for example U.sup.235, PU.sup.239, etc., which will produce a tremendous quantity of energy by reacting with neutrons. The nuclear fuel materials are not usually inserted with their surfaces exposed in the core; they are usually inserted within a wrapper tube containing a predetermined number of metal tubes such as stainless steel tubes, each of which contains the nuclear fuel material therein so as not to directly contact the nuclear fuel with the coolant that circulates throughout the core. The fuel assemblies including the wrapper tube having the predetermined number of metal tubes are commonly deformed arcuately or bent arcuately during operation of the nuclear reactor because of the materials being eradiated by a large quantity of fast neutrons. The degree of this bend or deformation varies in accordance with the integrated magnitude of eradiation by the neutrons, and the amount of the bend often reaches the magnitude of 40 to 50mm at the top of the fuel assembly according to a calculated result obtained with a formula commonly used for this purpose, in the case where the fuel assembly for a practical reactor is exchanged once in 6 months.
In addition to the above-mentioned fuel assemblies, a plurality of neutron shields, control rods, and blanket fuel assemblies are associated in the reactor core. All of these elements, including the fuel assemblies, may be referred to as core elements. Gaps of 3 to 5mm between the core elements are generally kept so that they may be easily pulled out or removed from the reactor core. When the core elements such as the fuel assemblies, the neutron shields, etc., are bent arcuately as above-mentioned, these gaps will disappear due to the bending, which will bring about many bad results, for example difficulty in inserting safety rods or control rods, impossibility of fuel exchanges, or blockages of the passage of the coolant. Therefore, it is desirable to prevent the fuel assemblies, control rods, neutron shields and the like core elements from bending in this manner.